1. Field of the Invention
The present invention relates to a projection exposure method used for forming a hole pattern.
2. Background Art
Recently, photolithography has made a dramatic advance. The numerical aperture (NA) of lenses has increased, the wavelength of the exposure light has been shortened, and thus, the resolution has been improved.
However, the increased NA of lenses and the shortened wavelength of the exposure light have led to reduction of the depth of focus (DOF), so that the practical resolution has not been significantly improved.
Thus, there is a demand for a technique of improving the DOF. For example, there is a technique of improving the resolution that involves sub-resolution assist features (SRAF), which are auxiliary patterns having a resolution equal to or less than the resolution limit, formed in a mask (reticle).
For example, a conventional projection exposure method uses an illumination intensity distribution in which the intensity is higher in the vicinity of apexes of an octagon (see Japanese Patent Laid-Open No. 5-47626, for example).
However, for the conventional projection exposure method described above, neither particular projection pattern arrangement nor particular SRAF arrangement is disclosed that allows efficient use of the illumination intensity distribution in which the intensity is higher in the vicinity of apexes of an octagon.